Cream together the butter and sugar until white and fluffy.,Add egg and beat well.,Sift together flours, baking powder and salt.,______,Mix in the flour and milk alternatively into the egg, starting and ending with the flour.,Fill 12 paper cupcake cases.,Bake at 180°C until golden and the cakes are springy.,Transfer to a wire wrack to cool and ice with plain butter icing (icing sugar, butter and hot water to make a smooth and fluffy icing).